In a copier, a printer or any other machine in which an image is created using a liquid such as an ink, dispersed particles in the liquid may settle when the liquid is not regularly agitated. For instance, pigment particles of an ink suspension may settle over time if the ink is not in motion. This will result in a reduced image quality and might even result in clogging of nozzles in a printhead used to create said images.
To agitate the liquid in a printer, for example to maintain the suspension of an ink, the liquid flow path in a printer is circulated regularly. This can be seen for instance in patent application WO 2013/150396 and patent U.S. Pat. No. 8,544,991.
The printing unit in the known art is a page wide printing unit to encompass the width of the medium to be printed on. All the printheads in the printing unit for a single color are connected to a single liquid handling system. Thus the liquid can only be circulated through all the printheads at the same time.
Therefore, the printing unit disclosed in the prior art is only suitable for circulation of liquid to agitate the liquid in a maintenance mode to prevent any printing deficiencies. This creates a loss in productivity.
It is therefore a disadvantage of the printing unit known from the prior art that the circulation of the liquid can only be performed while the printer is not in a printing mode, leading to a loss in productivity.
Furthermore, even if the liquid circulation in a printing unit according to the prior art would be performed in a printing mode (i.e. during printing an image), unequal liquid consumption by the individual printheads of the printer configuration of the known art may cause different pressures in each printhead. This creates a preferred flow of the liquid through the printhead having the highest liquid consumption due to pressure in this printhead being lower than the printheads where the liquid consumption is lower. The risk of settling of dispersed particles is the smallest in the printhead having the highest liquid consumption when compared to the other printheads.
Therefore the agitation of the liquid will differ in each printhead when operated in a printing mode and an equal suspension of dispersed particles in the liquid flowing through each individual printheads cannot be maintained or at least not guaranteed in said printing mode.
Thus, a maintenance mode is required to agitate the liquid in each individual printhead. The maintenance frequency, meaning the amount of times circulation of liquid to agitate the liquid is performed, will thus be determined by the printhead where the agitation is the most necessary due to the flow though this printhead being the smallest.
It is therefore an object of the present invention to overcome or at least mitigate above stated disadvantages by providing sufficient agitation in each of the printheads of a printhead array such that settling of dispersed particles is prevented and the maintenance frequency reduced.